The present invention relates generally to data hiding techniques, and more particularly, to visual data hiding techniques for a refined human visual model.
The escalating success of the Internet has allowed easy access to electronic data, which has also introduced problems regarding how to protect the electronic data. Many techniques have been proposed regarding the security issue over the last several years. One of these techniques introduces a digital watermarking of electronic data, which enables copyright protection of digital images. The digital watermarking technique, however, alters the perceived quality of electronic content. Therefore, it has been a challenging problem to properly reduce the watermark to protect the perceptual quality of the visual data while providing security. In particular, previous approaches tend to not be effective in eliminating or at least substantially reducing ringing effects on edges of image data.
Previous approaches utilize visual data hiding models to reduce the watermark to protect the perceptual quality of the image or video data. For example, Podilchuk-Zeng in Image Adaptive Watermarking Using Visual Models, IEEE Journal Selected Areas of Communication (JSAC), vol. 16, No. 4, May, 1998 discloses a frequency masking model for reducing artifacts appearing in the visual data. The method in Podilchuk-Zeng involves embedding the block discrete cosine transform (DCT) domain for image or video data and adjusting the watermark strength in each block based on the block-DCT domain frequency masking model. But they do not distinguish edge from texture. This leads to either ringing artifacts when work is strong or less robustness and less data hiding capacity when the strength of work is kept low to avoid artifacts. Tao-Dickinson in Adaptive Watermarking in the DCT domain, ICASSP 1997, proposed to apply block classification to reduce artifacts. Tao classifies image blocks into six categories, namely, edge uniform with moderate intensity, uniform with either high or low intensity, moderately busy, busy and very busy, in descending order of visual sensitivity against noise. Tao, then, respectively adjusts watermark strength in respectively ascending order. The Tao algorithm becomes rather complex as, for example, it enumerates various situations for horizontal edge, vertical edge, and diagonal edges across two regions of either uniform-texture or uniform-uniform and checks all the situations for each block. This approach suffers such disadvantages as (but not limited to) not being efficient in eliminating ringing effects on edges.
The present invention overcomes the aforementioned disadvantages and others. In accordance with the teaching of the present invention, the present invention receives an image or video file. The first step of the present invention is frequency masking wherein the image or video data is divided into blocks of smooth regions and blocks of non-smooth regions and preliminary just-noticeable difference of each frequency coefficient is obtained. The second step is edge detection wherein the non-smooth regions are divided into texture blocks and edge blocks. The third step is preferably used to determine which blocks of the regions are substantially proximate to blocks of smooth regions.
The image or video data is then adjusted by applying a different strength of watermark in association with the type of each block. Generally, a weaker strength of a watermark signal is applied to edge blocks than texture blocks. A weaker watermark signal is also applied to blocks that are adjacent to smooth regions. Thus, the present invention provides a more efficient and effective imperceptible data hiding method and apparatus that includes, but is not limited to, reducing ringing effects on edges that are very likely to be introduced by the conventional block DCT domain embedding approach for image and video.